Heatsink for electrical circuitry

ABSTRACT

A heatsink assembly including a substrate having an active circuitry, at least one cavity located adjacent to at least one heat producing element of the active circuitry, at least one vessel sealably coupled to said substrate in fluid communication with the at least one cavity, and a phase change material (PCM) contained inside the vessel. The vessel and at least one cavity are configured to facilitate migration of the PCM from the vessel into the at least one cavity for absorbing heat produced by the at least one heat producing element of the active circuitry.

TECHNOLOGICAL FIELD

The present invention is generally in the field of heatsinking andcooling systems, and particularly relates to phase change material (PCM)based heatsinking.

BACKGROUND

High power electrical/electronic circuitries can generate substantialamounts of heat during operation, causing overheating that can damagethe circuitries, or deteriorate their reliability, if proper coolingand/or heatsinking is not applied. For example, high power amplifiers(HPA) used for beaming microwave bursts e.g., as used in satellitecommunication and radar systems, can experience very high poweractivation bursts resulting in abrupt heating of the amplifyingcircuitries. Conventionally, fluid-cooled (e.g., by air or water)heatsinks (e.g., plate/fin/conduction path radiators) are thermallycoupled to the packaging of the HPA circuitries to dissipate anddistribute the heat thereby produced. However, electronic circuitriesare becoming compactly smaller and more powerful, thus yielding highlyconcentrated heat sources formed by the high power circuitries, whichaggravates the cooling problem, particularly under the growing demandfor dense packaging, low weight, and operation in harsh environments.

The conventional fluid cooled heatsink solutions can be effective inapplications wherein the produced heat is uniformly distributed acrossthe top surface of the semiconductor die. However, as the electroniccomponents are diminished in size, the conventional fluid cooledheatsink solutions are becoming less effective, since the significantamounts of the heat is produced in small discrete areas of the ICdensely populated by the high-power circuitries, resulting insignificantly high temperatures evolving in small discrete areas of theIC substrate. Since the high heat producing spots are discretelydistributed over the area of the IC substrate, only small amounts ofheat can be dispersed by the fins at the extremities (away from the heatsource) of the heatsink, such that standard heatsinks cannot effectivelycool the IC.

A possible attempt to overcome this problem suggests spreading the heatmore efficiently through the base of the heatsink. For example, in someof the solutions used nowadays heat pipes (also known as vapor chambers)are embedded in the heatsink to improve heat dispersion from thecondensed high-power circuitry areas to the extremities. Though heatpipe techniques can somewhat mitigate problems associated withdistribution of heat in heatsink devices, they are not so effective whenexcess amounts of heat needs to be quickly removed from discretelocations on a surface of a high frequency IC (>1 GHz).

For example, temperature control is critical to the performance of radarsystems, since the electrical performance of the HPAs decreases as theirtemperatures are increased. Hence, radar system are typically requiredto maintain the temperatures of the HPAs junctions below about 150° C.,and guarantee that the temperature variations between the modules do notexceed approximately 10° C., to assure reliability. These requirementscan be theoretically achieved by reducing the duty cycle, and/or thepulse width, of the radar system, and/or using powerful coolingequipment, which is inevitably costly in terms of weight, size, andmonetary price, and usually not so reliable. In practice, radar systemsnowadays require some combination/tradeoff of these temperature controlschemes to guarantee continuous reliable operation.

Some heatsink/cooling techniques knows from the patent literature arebriefly described hereinbelow:

U.S. Pat. No. 6,848,500 discloses an apparatus for reducing peaktemperatures and thermal excursions, of semiconductor devices,particularly in pulsed power applications. The apparatus comprisesthermally coupling phase change material (PCM) to the dissipatingsemiconductor device. PCM absorbs heat and stays at a constanttemperature during its phase change from solid to liquid. The PCMmelting point is chosen so that it is just below the temperature thedevice would otherwise achieve. When the device approaches the maximumtemperature, the PCM melts, drawing heat from the device and loweringthe device's peak temperature. As the device stops dissipating, afterits pulse period, the PCM material solidifies releasing the heat itabsorbed. The apparatus lowers the peak temperature by absorbing heatwhen the device is dissipating. The apparatus also keeps thesemiconductor device from cooling off as much as it would cool withoutthe apparatus, as the PCM material releases heat during the part of thecycle when it is re-solidifying, i.e., when the pulse power is off. Bylowering the peak temperature the device achieves, and increasing thetemperature of the device when it is in the off portion of its pulsedpower cycle the temperature excursions of the device during operationare reduced. By reducing the temperature swings, that the device seesduring operation, the thermal stress is reduced and the reliability ofthe device is improved.

US Patent Publication No. 2002/033247 describes a device comprising aphase change material arranged in or on a heat sink element in such away that significant heat flow from a central processing unit (CPU) viaa support only if the heat sink exceeds the phase change temperature ofthe phase change material, which thus ensures that the phase changematerial only absorbs the output peaks from the CPU.

International Patent Publication No. WO 2004/109798 describes a methodfor thermally protecting electronic units in an electronic device,particularly in a mobile radio device, with heat-generating electricalunits (heat sources), particularly with electrical components andcircuits. According to the invention, the heat-generating electricalunits are brought into working contact with a substance system (heatsink), which has a phase-change temperature that is near a predeterminedoperating temperature of the electronic device.

GENERAL DESCRIPTION

The present application provides techniques and structures exploitingthe properties of PCMs to absorb heat and maintain a substantiallyconstant temperature during their phase change, for heatsinking heatproducing regions of integrated circuits (ICs). The inventor hereoffound out that high-power ICs can be effectively cooled using PCM topump heat directly from the spots/regions of the substrate of the ICwherein heat producing circuitry junctions are densely embedded, andletting the heated PCM to migrate away from the substrate into aheatsink vessel (also referred to herein as PCM vessel) for condensationand dispersion of the heat thereby dissipated. This novel approach canthus surgically withdraw heat substantially directly from the hotspots/regions of the IC substrate, rather than from its external surfacearea (as commonly done nowadays), and thereby quickly and effectivelydistribute and disperse the excess heat produced at relatively smalldiscrete spots/regions of the IC substrate over larger surface areas ofthe heatsink vessel, that can be then easily cooled using conventionalcooling techniques (e.g., using plate/fin/conduction-path radiatorsand/or a streamed coolant).

In order to effectively sink heat from the heat producing spots/regionsdensely populated by high-power circuitries in an integrated circuitdie, embodiments disclosed herein are designed to allow a fluidic PCM tomigrate into the substrate of the IC and directly contact, or reside inclose proximity to, regions of the substrate (e.g., Silicon, GalliumArsenide, or suchlike) in which the active heat producing components areembedded. This is achieved in some embodiments by forming at least onelumen or channel in the substrate of the IC and fluidly coupling thelumen/channel to a heatsink vessel containing a PCM. The heatsink vesselis configured to enable the PCM to at least partially propagate into thelumen/channel formed in the substrate of the IC, to thereby absorb heattherefrom and undergo a phase change process, and receive back andcondense the heated PCM thereinside.

Optionally, but in some embodiments preferably, the PCM is a fluidicPCM, such as but not limited to water, configured to propagate in aliquid state at least partially into the lumen/channel formed in thesubstrate of the IC and absorb heat therein, change into a gaseous stateonce reaching a determined threshold temperature, and migrate undergaseous pressure forces evolving inside the lumen/channel back into theheatsink vessel for condensation.

In order to effectively remove heat directly from discrete heatproducing regions of the substrate of the IC, the at least onelumen/channel is formed in some embodiments along at least one heatproducing region of the substrate containing heat producingcircuitries/semiconductor junctions of the IC (e.g., accommodatingactive gates/transistors). The heatsinking can be maximized by formingthe at least one lumen/channel in close proximity to, and in someembodiments directly underneath the, active semiconductor junctions ofthe substrate e.g., underneath die regions comprising high powertransistors.

Optionally, but in some embodiments preferably, the heatsink vessel isat least partially filled with a porous medium (e.g., sintered metal,glass, or ceramic material) configured to contain the fluidic PCM in itsliquid state, and cause capillary motion (capillary action) of theliquid PCM therethrough and into the at least one lumen/channel formedin the substrate of the IC. In some possible embodiments the at leastone lumen/channel is also at least partially filled with a porous medium(e.g., sintered metal, glass, or ceramic material) configured to causecapillary motion of the liquid PCM therethrough.

Optionally, but in some embodiments preferably, the at least onelumen/channel and its coupling to the porous medium are configured topermit circulation of the fluidic PCM therebetween, as describedhereinbelow.

At least some portion of the PCM introduced by capillary motion throughthe porous medium into the at least one lumen/channel formed in thesubstrate of the IC contacts, or resides in close proximity to, the heatproducing regions of the IC substrate, and thus absorbs the heatproduced by the IC circuitry during its operation, such that when acertain temperature of the substrate is reached, the PCM undergoes aphase change process and at least some portion of the PCM in the atleast one lumen changes into a gaseous state, thereby absorbing moreheat from the IC substrate while maintaining a substantially constanttemperature level of the substrate i.e., the substrate temperature ismaintained within a range about (slightly above or below) apredetermined threshold temperature level.

As more PCM is changed into a gaseous state, increased pressureconditions evolving in the at least one lumen/channel cause the gaseousPCM to propagate along the lumen/channel and migrate at peripheralregions thereof back to the porous medium contained inside the heatsinkvessel, to condense back into liquid state thereinside, and draw newliquid PCM through the porous medium towards the at least onelumen/channel for absorbing more heat from the substrate of the IC. Inthis way the PCM is circulated in liquid state through the porous mediuminto the at least one lumen/channel, and in gaseous state through the atleast one lumen/channel back into the heatsink vessel, therebycontinuously removing heat form the substrate of the IC to the heatsinkvessel, and therefrom to the external environment/atmosphere, andreducing the temperature of the substrate and its IC. Once thetemperature of the substrate of the IC is reduced to a level below thephase change temperature threshold, the phase change process terminates,which also terminates the circulation of the PCM.

The heatsink vessel can be sealably attached to the substrate of the ICin fluid communication with the at least one lumen/channel formed in thesubstrate. For example, and without being limiting, one or more heatsinkvessels, each containing a porous medium and a fluidic PCM, can besealably attached at one or more respective sides of heat producingcomponents of an IC, and/or underneath them. In some possibleembodiments one or more cavities, each containing porous medium andfluidic PCM, are formed in the IC substrate in respective sides of heatproducing components of an IC, and/or underneath them.

The heatsink techniques disclosed herein can thus provide a passivethermal ground used to surgically withdraw heat from discrete smallregions of a substrate of a IC densely populated by heat producingjunctions, and reduce their temperatures by about 20° C. to 40° C.,optionally 25° C. to 35° C., and in certain embodiments by about 30° C.,without requiring additional cooling equipment/elements (e.g., withoutexternally applying cooled fluids). This heat reduction can be thustranslated into an overall weight reduction of systems, by diminishing,or altogether abolishing, the active cooling systems that high-powersystems are usually equipped with, and/or into improved reliabilitye.g., mean time between failures (MTBFs) can be increased by about 800%,and/or by increasing performance e.g., in terms of increased duty cycle,and/or pulse width, and/or transmission ranges.

One inventive aspect of the subject matter disclosed herein relates to aheatsink assembly comprising a substrate (e.g., made of a semiconductingmaterial, such as, but not limited to, Gallium-Arsenide or Silicon)having an active circuitry. The substrate comprises at least one cavitylocated adjacent to at least one heat producing element of the activecircuitry, at least one vessel sealably coupled to the substrate influid communication with the at least one cavity, and a phase changematerial (PCM) contained inside the vessel. The vessel and at least onecavity configured to facilitate migration of the PCM (e.g., by capillaryaction/motion) from said vessel into the at least one cavity forabsorbing heat produced by the at least one heat producing element ofthe active circuitry. In some embodiments the at least one vessel andthe at least one cavity are configured to circulate the PCMtherebetween, to thereby transfer the heat absorbed by the PCM to the atleast one vessel. Optionally, but in some embodiments preferably, thePCM comprises water.

The at least one vessel comprises in some embodiments a porous mediumconfigured to facilitate migration of the PCM therethrough towards theat least one cavity in the substrate. Optionally, the at least onecavity comprises a porous medium configured to facilitate migration ofthe PCM inside the substrate towards the at least one heat producingelement. The at least one of the at least one vessel and the porousmedium can be configured to condense the heated PCM. In some embodimentsthe porous medium(s) define pore sizes in a range of 100 to 70,000nanometer. The porous medium comprises in some embodiments a sinteredmaterial e.g., made of metal or ceramic materials, or a combinationthereof.

The substrate is attached in some embodiments to a carrier board. Thecarrier board comprising at least one via configured to communicatebetween the at least one vessel and the at least one cavity andfacilitate migration of the PCM therethrough from the at least onevessel into the at least one cavity. A plurality of substrates, eachhaving a respective active circuitry and at least one cavity locatedadjacent to at least one heat producing element of said respectiveactive circuitry, can be attached to the carrier board, and the carrierboard can comprise a respective at least one via configured tocommunicate between the at least one vessel and the at least one cavityof a respective substrate of the plurality of substrates. In someembodiments a plurality of the at least one vessel are used, where eachof the plurality of vessels contains PCM and being sealably coupled toat least one of the plurality of substrates in fluid communication withits at least one cavity through at least one of the vias of the carrierboard. Optionally, and in some embodiments preferably, the assemblycomprises a respective vessel for each one of the plurality ofsubstrates.

The at least one via can be configured to facilitate capillary motion ofthe PCM therethrough. For example, a diameter of the at least one via insome embodiments is in a range of 10 to 100 micrometer.

Optionally, the carrier board comprises at least one cavity configuredto receive the PCM from the at least one vessel and facilitate migrationof the PCM therethrough to the at least one cavity of a substratethrough the at least one via of the carrier board. The at least onecavity of the carrier board may comprise a porous medium configured tofacilitate the PCM migration therethrough. The porous medium containedin the at least one cavity of the carrier board can be made from thesame materials, and using the same techniques, as described hereinaboveand hereinbelow, and also can define the same pore sizes.

In some embodiments the carrier board comprises at least one coatinglayer applied over a surface area thereof. The at least one via can beconfigured to pass through the at least one coating layer. The at leastone coating layer can be electrically coupled to the active circuitry,and/or configured to disperse heat removed from the substrate by thePCM. The at least one vessel can be thus sealably attached over the atleast one coating layer of the carrier board.

The at least one vessel comprises in some embodiments one or morematerials having good thermal conductivity e.g., Copper, Gold, Aluminum,Silver, or a combination thereof. In some embodiment the at least onevessel comprises a material having thermal conductivity greater than 100w/(m·K).

Optionally, the depth of the at least one cavity of the substrate is ina range of 55% to 85% of a thickness of said substrate. For example, adistance of an edge of the at least one cavity from the at least oneheat producing element of the active circuitry is in some embodiments ina range of 20 to 50 micrometer. A width of the at least one cavity inthe substrate ca be in a range of 5 to 70 micrometer.

Another inventive aspect of the subject matter disclosed herein relatesto a method for dispersing heat produced by active circuitry embeddedin, or on, a substrate. The method comprising forming at least onecavity in said substrate, placing PCM inside at least one vessel, andsealingly coupling between said at least one vessel and said at leastone cavity. The method may comprise placing a porous medium inside theat least one vessel. The porous medium can be configured to hold atleast some portion of the PCM and facilitate migration thereof towardsthe at least one cavity. Optionally, the method comprises placing aporous medium inside the at least one cavity.

The coupling comprises in some embodiments forming at least one via in acarrier board, sealingly attaching the substrate to the carrier boardsuch that it's at least one cavity is in fluid communication with the atleast one via, and sealingly attaching the at least one vessel to thecarrier board such that the at least one via communicates between the atleast one vessel and the at least one cavity. The method can compriseforming a plurality of vias in the carrier board, sealingly attaching aplurality of substrates to the carrier board, each of the plurality ofsubstrates having a respective active circuitry and at least one cavity.The substrates can be attached to the carrier board such that the atleast one cavity of a respective substrate of the plurality ofsubstrates communicates with the at least one vessel through arespective at least one via of the carrier board.

The method comprises in some embodiments placing a PCM in a plurality ofvessels, sealingly coupling each of the plurality of vessels to at leastone of the plurality of substrates in fluid communication with its atleast one cavity through at least one of the vias of the carrier board.Optionally, but in some embodiments preferably, the method comprisescoupling a respective vessel to each one of the plurality of substrates.

In some possible embodiments at least one cavity is formed in thecarrier board. The at least one cavity configured to receive the PCMfrom the at least one vessel and facilitate migration thereof to the atleast one cavity of a substrate through the at least one via of thecarrier board. The method can also comprise placing a porous medium inthe at least one cavity of the carrier board.

Optionally, the method comprises applying at least one coating layerover a surface area of the carrier board, forming the at least one viato pass through said at least one layer, and thermally coupling betweensaid at least one coating layer and the at least one vessel.

Yet another inventive aspect of the subject matter disclosed hereinrelates to a heatsink vessel comprising a PCM and a porous mediumconfigured to hold at least a portion of the PCM and facilitatemigration thereof therethrough. The heatsink vessel having at least oneopening configured to sealingly attach to a substrate and facilitatemigration of the PCM therethrough towards the substrate for absorbingheat from the substrate by the PCM. Optionally, the heatsink vesselcomprises one or more thermally conducting materials. Thus, the heatsinkvessel can be configured to absorb heat from the PCM by at least one ofthe porous medium and the vessel.

A heatsink assembly can thus comprise at least one heatsink vesselaccording to any of the embodiments disclosed herein, and a carrierboard attachable to at least one substrate having an active circuitry.The carrier board comprises at least one via, and the at least oneheatsink vessel sealingly coupled to the at least one via to facilitatemigration of at least a portion of the PCM therethrough. Optionally, thecarrier board comprises at least one cavity configured to facilitatemigration of at least a portion of the PCM therethrough. The at leastone cavity in the carrier board may contain a porous medium configuredto facilitate migration of at least a portion of the PCM therethrough.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carriedout in practice, embodiments will now be described, by way ofnon-limiting example only, with reference to the accompanying drawings.Features shown in the drawings are meant to be illustrative of only someembodiments of the invention, unless otherwise implicitly indicated. Inthe drawings like reference numerals are used to indicate correspondingparts, and in which:

FIGS. 1A to 1C schematically illustrate a heatsinking techniqueaccording to some possible embodiments, wherein FIG. 1A demonstratessealing a cavity/lumen formed in a substrate of an IC by a PCM vessel;FIG. 1B shows a possible embodiment wherein the cavity in the substrateis at least partially filled with a porous medium, and

FIG. 1C demonstrate an operational state wherein the PCM is circulatedbetween the cavity in the substrate and the PCM vessel;

FIG. 2A and FIG. 2B schematically illustrate structures for heatsinkinga plurality of ICs according to some possible embodiments;

FIG. 3 schematically illustrates a multichannel structure formed in someembodiments in a substrate for heatsinking multiple circuitries of anIC;

FIGS. 4A to 4C schematically illustrate structures for heatsinking aplurality of ICs according to some other possible embodiments; and

FIG. 5 is a flowchart schematically a heatsinking process according tosome possible embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS

One or more specific embodiments of the present disclosure will bedescribed below with reference to the drawings, which are to beconsidered in all aspects as illustrative only and not restrictive inany manner. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. Elements illustrated in the drawings are notnecessarily to scale, or in correct proportional relationships, whichare not critical. Emphasis instead being placed upon clearlyillustrating the principles of the invention such that persons skilledin the art will be able to make and use them, once they understand theprinciples of the subject matter disclosed herein. This invention may beprovided in other specific forms and embodiments without departing fromthe essential characteristics described herein.

An object of the embodiments disclosed herein is to sink heat producedin a die by active electrical components, such as HPAs. For this purposechannels/lumens are formed in a substrate (e.g., semiconductor)carrying/embedding the circuitry. The channels/lumens can be formed inthe substrate under heat producing areas/junctions. A porous mediumcontaining a flowable phase change material (PCM e.g., water) is thencoupled to the substrate in fluid communication with thechannels/lumens. The PCM and porous medium are configured to introduceat least some portion of the PCM, in liquid state, into thechannels/lumens formed in the substrate by capillary motion. Duringactivation peaks of the electrical components the PCM absorbs theproduced heat and changes into a gaseous phase that is flown back intothe porous medium due to increase of pressure in the channels/lumens.The gaseous PCM is condensed in the porous medium and circulated backinto the channels/lumens to sink more heat from the circuitries.

The porous medium and the PCM can be housed in a heatsink vesselsealably attached to the substrate. Optionally, but in some embodimentpreferably, the heatsink vessel with the porous material and PCMcontained thereinside is attached to an intermediate layer (e.g.,semiconductor layer, printed circuit board made of ceramic or organicmaterial, or suchlike) to which the substrate of the IC is attached. Theintermediate layer comprises in some embodiments one or more vias(capillary pass-through holes) formed therein for communicating betweenthe heatsink vessel and the at least one lumen formed in the substrate,for passage of the fluid PCM therethrough.

FIG. 1A exemplifies construction of a heatsink assembly 10 configured toremove heat from a substrate 11 (e.g., made from a semiconductormaterial, such as Silicon or Gallium-Arsenide) of an IC. In someembodiments at least one open channel 11 c (also referred to herein ascavity or lumen) is formed in a bottom side of the substrate 11.Optionally, but in some embodiments preferably, the at least one openchannel 11 c is formed underneath a region of the substrate 11comprising a plurality of active gates/junctions 11 a (also referred toherein as heat producing element e.g., amplifier/transistor) of the IC.The at least one open channel 11 c can have a substantial depth D, inorder for it to reach close proximity to the active gates/junctions 11 aof the IC. For example, in some possible embodiments the depth D of thechannel 11 c is in a range 60% to 80% of the thickness T of thesubstrate 11, optionally about 70% of the thickness T of the substrate11 e.g., depth D of 70 micrometer in a substrate having thickness T of100 micrometer.

The width of the channel 11 c is configured in some embodiments tofacilitate capillary motion of the PCM 14 towards the activegates/junctions 11 a. Thus, the width of the channel 11 c can be about 5to 75 micrometer. In some embodiments a plurality of elongated andsubstantially parallel channels 11 c are formed in the substrate 11e.g., as exemplified in FIG. 3.

The at least one open channel 11 c is sealingly closed by attaching acup-shaped heatsink vessel 13 over its bottom side opening 11 n. Theheatsink vessel 13 is configured to hold a liquid PCM 14 thereinside,and to cause migration of at least some portion of the PCM 14 towardsand into the at least one open channel 11 c. The heatsink vessel 13 canbe fabricated from materials having good/high thermal conductivity, suchas, but not limited to Copper, Carbal, aluminum, Silicon, AluminumNitride, and suchlike. The heatsink vessel 13 can be configured to holdPCM volume of about 1 to 10 cm³.

Optionally, but in some embodiments preferably, the heatsink vessel 13comprises a porous medium 13 p configured to hold the PCM 14 in itspores and cause capillary motion thereof through the pores, towards andthrough the bottom opening 11 n of the at least one open channel 11 c.The pores of the porous medium 13 p can be configured to permitcapillary action of the PCM in its liquid state therethrough. Forexample, in the embodiments utilizing water as PCM the pores of theporous media 13 p can be generally in a range of about 5 to 100micrometers. In some possible embodiments the porous medium 13 p is madeof sintered metal, glass, silicon, or ceramic material. After placingthe porous medium 13 p inside the heatsink vessel 13 and introducing thePCM 14 thereinto, the heatsink vessel 13 is sealably attached (e.g.,using thermally conducting adhesive, such as, but not limited to, epoxyglue, solder, brazing, to the substrate 11 such that its opening 13 ncommunicates with the opening(s) 11 n of the at least one open channel11 c.

FIG. 1B exemplifies a heatsink assembly 10′ according to some possibleembodiments, wherein the at least one open channel 11 c formed in thesubstrate 11 of the IC is filled with a porous medium 11 p. As seen, theheatsink assembly 10′ is principally similar in structure and operationto the heatsink assembly 10 of FIG. 1A. The porous medium 11 p of the atleast one open channel 11 c can be configured to facilitate capillaryaction of the PCM 14, and thereby cause further migration of the PCM 14towards the active gates/junctions 11 a of the IC. In some embodimentsthe pore size of the porous medium 11 p is in same range as of poresizes of the porous medium 13 p, and it can be also prepared using sameor similar materials. In this embodiment upon sealably attaching theheatsink vessel 13 to the substrate 11, porous medium continuity isobtained by the porous mediums 13 p and 11 p, extending from theinterior of the heatsink vessel 13 into the at least one open channel 11c. Accordingly, in this embodiment the PCM 14 can capillary migrate allthe way from the heatsink vessel 13 to the upper face 11 u of the atleast one open channel 11 c through the porous mediums 13 p and 11 p,and directly absorb therefrom the heat generated by the activegates/junctions 11 a.

FIG. 1C shows the heatsink assembly 10 after attaching the heatsinkvessel 13 to the substrate 11 of the IC. Circulation of the PCM 14according to some possible embodiments is demonstrated by the arrows 14q, 14 g and 14 d. Particularly, some portion of the liquid PCM 14capillary migrates (14 q) into the at least one channel 11 c and absorbsthe heat produced by the active gates/junctions 11 a. The PCM 14 heatedin the at least one channel 11 c change into gaseous state (14 g) andspread thereinside and absorb more heat from the substrate 11, withoutchanging its temperature to thereby maintain the temperature of thesubstrate 11 substantially within the phase changing temperature rangeof the PCM 14. As the pressure inside the channel 11 c increase due tothe heated gaseous PCM (14 g), portions of the gaseous PCM (14 d)propagate back into the heatsink vessel 13 at the boundaries of the atleast one open channel 11 c. The heat of the gaseous PCM (14 d)introduced into the heatsink vessel 13 is transferred to the porousmedium 13 p and the walls of the heatsink vessel 13, and thereby cooledand condense back into a liquid state PCM capillary propagating (14 q)into the at least one channel 11 c to absorb more heat from the activegates/junctions 11 a of the substrate 11.

FIG. 2A schematically illustrate a heatsink assembly 20 configured forheatsinking substrates 11 of a plurality of ICs mounted onto a board 21(also referred to herein as IC board e.g., a printed circuit board—PCB,a Silicon substrate, an organic substrate, or suchlike. In this specificand non-limiting example, each IC substrate 11 is coupled to arespective heatsink vessel 13, comprising a PCM 14, through respectiveone or more vias 21 v (capillary pass-through bores). The vias 21 v areconfigured to facilitate capillary action for the liquid PCM 14 tomigrate therethrough from each heatsink vessel 13 into at least onechannel 11 c of a respective IC substrate 11 to absorb heat therefrom.Optionally, but in some embodiments preferably, the heatsink vessels 13also comprise porous media 13 p configured to facilitate the capillarymigration of the liquid PCM 14 to the respective channels 11 c. Inpossible embodiments one or more of the heatsink vessels 13 can beconfigured to couple to two or more of the IC substrates 11.

FIG. 2B shows a heatsink assembly 20′ which is principally similar instructure and operation to the heatsink assembly 20 of FIG. 2A, but itis different in that the board 21 in this embodiment comprises one ormore coating layers 15 applied on a bottom side thereof. As seen, inthis embodiment the vias 21 v formed in the board 21 also pass throughthe one or more coating layers 15 to form a continuous passage for thePCM 14 to capillary migrate from the heatsink vessels 13 to the at leastone channel 11 c of the respective substrates 11. In possibleembodiments the one or more coating layers 15 comprise an electricallyconducting material (e.g., Copper) electrically coupled to at least oneof the ICs of the active gates/junctions 11 a.

FIG. 2B depicts an embodiment wherein a single electrically conductingcoating layer 15 covers a surface area of the bottom side of the board21, and the heatsink vessels 13 are sealably attached to theelectrically conducting coating layer 15 over respective vias 21 v, tocommunicate with the channels 11 c of the substrates 11 therethrough. Insome embodiments wherein the one or more coating layers 15 comprisematerials having good thermal conductivity, such as metals, theheatsinking is further improved as the heat absorbed from the PCM 14 bythe walls of the heatsink vessels 13 also disperse in the one or morecoating layers 15 covering the surface area of the bottom side of theboard 21. Due to the larger surface area of the one or more coatinglayers 15, the heat absorbed therein can be quickly transferred to theexternal environment/atmosphere.

In some embodiments the diameter d of the vias 21 v is about 10 to 100micrometer.

FIG. 3 schematically illustrates a multichannel structure formed in someembodiments in a substrate 11′ for heatsinking active gates/junctions 11a′ of multiple ICs. In this non-limiting example a plurality of openchannels 11 c′ are formed in the substrate 11′ underneath activegates/junctions 11 a′ to allow the PCM to migrate to multiple regions inproximity to the active gates/junctions 11 a′ and dissipate the heatthey produce during operation. Heatsink vessels (not shown) can beaccordingly configured to enclose and seal the side openings of the openchannels 11 c′. Though the open channels 11 c′ are shown passing fromside to side in the substrate 11′, in some embodiments they are confinedwithin the side walls 11 w, such that they can be sealably closed bycup-shaped heatsink vessel (13), as exemplified hereinabove.

In this specific and non-limiting example the IC of the substrate 11′comprises four elongated and substantially parallel activegates/junctions 11 a′ regions, and the open channels 11 c′ pass in thesubstrate 11′ in a traversing direction substantially perpendicular tothe directions of the four active gates/junctions 11 a′ regions. Thoughthe substrate 11′ is shown comprising six traversing open channels 11c′, it can be configured to comprise any other suitable numbertraversing open channels 11 c′, which can be determined according to thelengths of the active gates/junctions 11 a′ regions and the widths W ofthe traversing open channels 11 c′. In some embodiments the width W ofthe traversing open channels 11 c′ is about 5 to 70 micrometer, and thedistance L between two adjacent open channels 11 c′ is about 40 to 100micrometer.

FIG. 4A schematically illustrates a heatsink assembly 30 configured todissipate and remove heat from active gates/junctions 11 a of aplurality of ICs. In this specific and non-limiting example at least oneelongated open channel 41 c is formed along a substantial length ofboard 21, under a plurality of substrates 11 in which activegates/junctions 11 a of a plurality of ICs are embedded. The heatsinkassembly 30 comprises in some embodiments a plurality of parallelelongated open channels 41 c, such as exemplified in FIG. 3 (designatedby reference numeral 11 c′). Each substrate 11 comprises achannel/cavity 11 c, and each channel/cavity 11 c is in fluidcommunication with the at least one elongated open channel 41 c throughat least one (capillary) via 41 v. The heatsink assembly 30 comprises acorresponding heatsink vessel 33 comprising PCM 14 and configured tosealably close the at least one elongated open channel 41 c.

The at least one elongated open channel 41 c and the at least one via 41v are configured to facilitate capillary motion of the PCM 14therethrough from the heatsink vessel 33 to the channels/cavities 11 cof the substrates 11. Accordingly widths of the at least one elongatedopen channel 41 c can be in the range (W) indicated hereinabove withreference to FIG. 3, and the diameters of the vias 41 v can be in range(d) indicated hereinabove with reference to FIGS. 2A and 2B. Optionally,but in some embodiments preferably, the heatsink vessel 33 comprises aporous medium 13 p filling a substantial portion, or all, of its volume.The porous medium 13 p configured to hold the PCM 14 and facilitatecapillary motion thereof into the at least one elongated open channel 41c.

FIG. 4B shows the heatsink assembly 30 after sealably attaching theheatsink vessel 33 to the board 21. In this state the PCM 14 cancapillary migrate from the heatsink vessel 33 into the channels/cavities11 c of the substrates 11 and absorb the heat produced by the activegates/junctions 11 a, as described hereinabove in detail.

FIG. 4C shows another possible embodiment of a heatsink assembly 30′comprising at least one open channel 41 c′ filled with porous medium 23p. The heatsink assembly 30′ is principally similar to the heatsinkassembly 30 of FIGS. 4A and 4B, but provides continuous porous mediumbetween the heatsink vessel 33 and the at least one open channel 41 c′,formed by the porous mediums 13 p and 23 p, for facilitating capillarymigration of the PCM 14 therethrough from the heatsink vessel 33 to thevias 41 v communicating the PCM 14 to the channels/cavities 11 c. Thereis thus no need in this embodiment to adjust the width of the at leastone open channel 41 c′ for capillary motion of the PCM 14, because it isfilled with the porous medium 23 p configured to guarantee capillarymigration of the PCM 14 therethrough. The porous mediums 13 p and 23 pcan be prepared from the same materials, and with the same geometricalproperties, as described hereinabove with reference to FIGS. 1A to 1Cand FIGS. 2A and 2B.

Optionally, the channels/cavities 11 c formed in the substrates 11 ofthe ICs shown in FIGS. 2A and 2B and FIGS. 4A to 4C, are also filledwith a porous medium (as exemplified din FIG. 1B). In some embodimentsthe board 21 comprises one or more layers (not shown in FIGS. 4A to 4C)electrically coupled to the ICs e.g., such as coating layer(s) 15 shownin FIG. 2B.

FIG. 5 shows a flowchart illustrating a heatsinking process 50 accordingto some possible embodiments. The process 50 starts in step 51, in whichone or more channels/cavities (11 c) are formed in substrates' (11) ofone or more ICs, and optional step 52 in which one or morechannels/cavities (41 c/41 c′) are formed in the IC board (21/21′). Theone or more channels/cavities (11 c) are preferably formed in thesubstrates (11) as close as possible to the active gates/junctions (11a) of the ICs, as exemplified hereinabove.

Next, in step 53, one or more vias (21 v/41 v) are formed in the ICboard (21/21′) at locations corresponding to the locations of the one ormore channels/cavities (11 c) formed in substrates (11). In step 54 oneor more PCM vessels (13/33) are filled with porous medium (13 p), and inoptional step 55 the one or more channels/cavities (11 c) formed in thesubstrates (11) are filled with porous medium (11 p). If one or morechannels/cavities (41 c/41 c′) are formed in optional step 52 in the ICboard (21/21′), in step 56 they are optionally filled with a porousmedium (23 p), if so needed.

In step 57 PCM (14) is introduced into the one or more PCM vessels(13/33), and in step 58 the fluid passages i.e., the vias (21 v/41 v)formed in the IC board (21/21′) and the optional channels/cavities (41c/41 c′) (if) formed in the IC board (21/21′), are sealably closed bythe one or more PCM vessels (13/33). In optional step 59 a coolant isstreamed over the PCM vessels (13/33) to remove heat absorbed thereinfrom the PCM (14) circulated during the operation of the ICs.

Terms such as top/upper, bottom/lower, front, back, right, left, sides,and similar adjectives in relation to orientation of the elements andcomponents of the assemblies shown in the figures refer to the manner inwhich the illustrations are positioned on the paper, not as anylimitation to the orientations in which the apparatus can be used inactual applications.

It should also be understood that throughout this disclosure, where aprocess or method is shown or described, the steps of the method may beperformed in any order or simultaneously, unless it is clear from thecontext that one step depends on another being performed first.

The heatsink techniques of the present application can be exploited,inter alia, for overall system weight and/or size reduction(s), increaseof system performance and reliability, and reduce in monetary costs,thereby providing less demanding high-power systems that can be mountedin new and less resourceful platforms. It is appreciated that certainfeatures of the subject matter disclosed herein, which are, for clarity,described in the context of separate embodiments, may also be providedin combination in a single embodiment. Conversely, various features ofthe disclosed subject matter, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination.

As described hereinabove and shown in the associated figures, thepresent invention provides heatsink assemblies configured to dissipateand distribute heat from electric/electronic circuitries, and relatedmethods. While particular embodiments of the disclosed subject matterhave been described, it will be understood, however, that the inventionis not limited thereto, since modifications may be made by those skilledin the art, particularly in light of the foregoing teachings. As will beappreciated by the skilled person, the invention can be carried out in agreat variety of ways, employing more than one technique from thosedescribed above, all without exceeding the scope of the claims.

For an overview of several exemplary features, process stages, andprinciples of the disclosed subject matter, the assemblies illustratedschematic ally and diagrammatically in the figures are intended forheatsinking electric/electronic circuitries. These heatsink assembliesare provided as exemplary implementations that demonstrates a number offeatures, processes, and principles used for removing heat fromcircuitries implemented in a substrate, but they are also useful forother applications and can be made in different variations. Therefore,the above description refers to the shown examples, but with theunderstanding that the invention recited in the claims below can also beimplemented in myriad other ways, once the principles are understoodfrom the descriptions, explanations, and drawings herein. All suchvariations, as well as any other modifications apparent to one ofordinary skill in the art and useful for heatsinking applications may besuitably employed, and are intended to fall within the scope of thisdisclosure.

The invention claimed is:
 1. A heatsink assembly, comprising: asubstrate having an active circuitry, said substrate comprises: at leastone cavity located adjacent to at least one heat producing element ofsaid active circuitry; at least one vessel sealably coupled to saidsubstrate in fluid communication with said at least one cavity; and aphase change material (PCM) contained inside said at least one vessel;wherein said at least one vessel and at least one cavity are configuredto facilitate migration of said PCM from said at least one vessel intosaid at least one cavity for absorbing heat produced by said at leastone heat producing element of said active circuitry.
 2. The heatsinkassembly of claim 1 wherein the at least one vessel and the at least onecavity are configured to circulate the PCM therebetween, to therebytransfer the heat absorbed by the PCM to the at least one vessel.
 3. Theheatsink assembly of claim 1, further comprising a porous mediumcontained inside the at least one vessel and configured to facilitatemigration of said PCM therethrough towards the at least one cavity inthe substrate.
 4. The heatsink assembly of claim 3 wherein at least oneof the at least one vessel or the porous medium is configured tocondense the heated PCM.
 5. The heatsink assembly of claim 3 wherein theporous medium defines pore sizes in a range of 100 nanometer to 70,000nanometer.
 6. The heatsink assembly of claim 3 wherein the porous mediumcomprises a sintered material.
 7. The heatsink assembly of claim 3wherein the porous medium comprises metal material, ceramic material, ora combination thereof.
 8. The heatsink assembly of claim 1, furthercomprising a porous medium contained inside the at least one cavity andconfigured to facilitate migration of the PCM inside the substratetowards the at least one heat producing element.
 9. The heatsinkassembly of claim 1, further comprising a carrier board to which thesubstrate is attached, said carrier board comprising at least one viaconfigured to communicate between the at least one vessel and the atleast one cavity and facilitate migration of the PCM therethrough fromsaid at least one vessel into said at least one cavity.
 10. The heatsinkassembly of claim 9, further comprising a plurality of substrates, eachhaving a respective active circuitry and at least one cavity locatedadjacent to at least one heat producing element of said respectiveactive circuitry, said plurality of substrates attached to the carrierboard, and said carrier board comprising a respective at least one viaconfigured to communicate between the at least one vessel and the atleast one cavity of a respective substrate of said plurality ofsubstrates.
 11. The heatsink assembly of claim 10, further comprising aplurality of the at least vessel, each of which contains PCM and beingsealably coupled to at least one of the plurality of substrates in fluidcommunication with at least one cavity thereof through at least one ofthe vias of the carrier board.
 12. The heatsink assembly of claim 11,further comprising a respective vessel for each one of the plurality ofsubstrates.
 13. The heatsink assembly of claim 9 wherein the at leastone via is configured to facilitate capillary motion of the PCMtherethrough.
 14. The heatsink assembly of claim 9 wherein a diameter ofthe at least one via is in a range of 10 micrometer to 100 micrometer.15. The heatsink assembly of claim 9 wherein the carrier board comprisesat least one cavity configured to receive the PCM from the at least onevessel and facilitate migration of the PCM therethrough to the at leastone cavity of a substrate through the at least one via of the carrierboard.
 16. The heatsink assembly of claim 15 wherein the at least onecavity of the carrier board comprises a porous medium configured tofacilitate the PCM migration therethrough.
 17. The heatsink assembly ofclaim 16 wherein the porous medium define pore sizes in a range of 100nanometer to 70,000 nanometer.
 18. The heatsink assembly of claim 16wherein the porous medium comprises a sintered material.
 19. Theheatsink assembly of claim 16 wherein the porous medium comprises metalor ceramic materials, or a combination thereof.
 20. The heatsinkassembly of claim 9 wherein the carrier board comprises at least onecoating layer applied over a surface area thereof, and wherein the atleast one via passes through said at least one coating layer.
 21. Theheatsink assembly of claim 20 wherein the at least one coating layer iselectrically coupled to the active circuitry.
 22. The heatsink assemblyof claim 20 wherein the at least one coating layer is configured todisperse heat removed from the substrate by the PCM.
 23. The heatsinkassembly of claim 20 wherein the at least one vessel is sealablyattached over the at least one coating layer of the carrier board. 24.The heatsink assembly of claim 1 wherein the PCM migration is achievedby capillary action.
 25. The heatsink assembly of claim 1 wherein the atleast one vessel comprises one or more materials having good thermalconductivity.
 26. The heatsink assembly of claim 25 wherein the at leastone vessel comprises a material having thermal conductivity greater than100 w/(m·K).
 27. The heatsink assembly of claim 25 wherein the vesselcomprises at least one of Copper, Gold, Aluminum, or Silver.
 28. Theheatsink assembly of claim 1 wherein the at least one cavity of thesubstrate exhibits a depth in a range of 55% to 85% of a thickness ofsaid substrate.
 29. The heatsink assembly of claim 1 wherein a distanceof an edge of the at least one cavity from the at least one heatproducing element of the active circuitry is in a range of 20 micrometerto 50 micrometer.
 30. The heatsink assembly of claim 1 wherein the atleast one cavity in said substrate exhibits a width in a range of 5micrometer to 70 micrometer.
 31. The heatsink assembly of claim 1wherein the substrate is made from a semiconducting material.
 32. Theheatsink assembly of claim 31 wherein the substrate is made ofGallium-Arsenide.
 33. The heatsink assembly of claim 31 wherein thesubstrate is made of Silicon.
 34. The heatsink assembly of claim 1wherein the PCM comprises water.